In auto cascade cryogenic cooling systems with multiple auto cascade stages, refrigerant gas mixes are used as the refrigerant, comprising component fluids to refrigerate in different stages of the auto cascade. The component fluids work at different refrigerant boiling temperature bands for each auto cascade stage. Such fluids are typically a mix of CFC, HFC, HCFC, fluorocarbons, hydrocarbons and natural gases. The utilization of such refrigerant mixes in auto cascade systems enables the achievement of ultra-low temperatures with good cooling performance.
Most refrigerant fluid mixes that work effectively using components with CFCs and/or HCFCs may be toxic, flammable, having high ODP and may have high global warming potential; all of which are factors that inhibit the increase of use of such mixes. Environmental concern over the accelerating deleterious effects on the ozone layer of the atmosphere has resulted in efforts in the industry to substantially reduce the use of CFC refrigerants. In some of the refrigerant mixes presently in use, two or more HCFC components are used, resulting in high ODP.
Adoption of non-CFC refrigerant mixtures and reduction of HCFC refrigerant components, faces difficulties in use such as discharge temperatures and pressures tending to be higher than desirable, causing lubricant carry-over and system problems; compressors typically run hot because of insufficient cooling, lubricants need change to enable proper performance and most mixtures are not drop-in replacements.
In other created refrigerant mixes the proportions of flammable and toxic gases, are high and could constitute cause for concern in regular use, mainly because of possible leaks in use and maintenance. Several prior arts are discussed hereunder:
U.S. Pat. No. 5,702,632 titled “Non-CFC refrigerant mixture” describes a refrigeration heat exchanger section useful in circulating a substantially non-CFC refrigerant mixture. However, the above invention uses a high proportion of a refrigerant that is quite flammable and uses R-142b, which is a CFC having high ODP and GWP.
U.S. Pat. No. 6,631,625 titled “Non-HCFC refrigerant mixture for an ultra-low temperature refrigeration system” describes a method and apparatus for a refrigeration heat exchanger section useful in circulating a substantially non-HCFC refrigerant mixture. However, this refrigerant mixture is mainly a refrigerant blend free of R-22 for use in ultralow temperature refrigeration meant for machines that use POE oils and cannot be used in older machines that use Alkylbenzene oils.
US 20010042379 titled “Refrigerant blend free of R-22 for use in ultralow temperature refrigeration” describes refrigerants containing R-22 replaced with new blends by using R-125 with R-124 and R-123, or R-125 with R-124 and R-218, or R-218 with R-124, in place of R-22. However, the above formulation contains more than one HCFC and has a high GWP.
US 20050103028 titled “Non-CFC refrigerant mixture for an ultra-low temperature refrigeration system” describes method and apparatus for a refrigeration heat exchanger section useful in circulating a substantially non-CFC refrigerant mixture. However, the above invention uses a high proportion of a refrigerant that is quite flammable. The component R-142b used in the above invention is a CFC, having high ODP and GWP.
US RE40627 titled “Nonflammable mixed refrigerants (MR) for use with very low temperature throttle-cycle refrigeration systems” describes refrigerants containing HCFC's replaced with new blends by using R-236fa and R-125, or R-125 with R-245fa, or R-236ea, or R-134a with R-236fa in place of HCFC's. However, the refrigerant mix of the above invention can be used only in auto cascade machines that use POE oils and are not a drop in replacement for machines using alkylbenzene oils.
Accordingly, there exists a need to provide a refrigerant mixture with very low ozone depletion potential combined with low global warming potential. The present invention aims at providing non-flammable, non-toxic refrigerant mixture having no CFC. In addition, there is a need to provide a refrigerant mixture that uses commercially available gases and which is compatible with most of the standard refrigeration oils and compressor materials.